Gaseous condensation in vacuum with plural refrigerants



Jan. 9, 1968 E. CARBONELL ETAL 3, 74.

GASEOUS CONDENSATION' IN VACUUM WITH PLURAL REFRIGERANTS Filed Oct. 5, 1964 Awn m! REVERS/A/G 1 4 CUUM CHAMBERS LCM/LE CflKdO/VEAL Mom/00E M4877 Arr-x United States Patent 3,362,174 GASEOUS CONDENSATION IN VACUUM WITH PLURAL REFRIGERANTS Emile Carbonell and Monique Martin, Sassenage, France, assignors to LAir Liquide Societe Anonyme pour IEtude et lExploitation des Procedes Georges Claude Filed Oct. 5, 1964, Ser. No. 401,371 Claims priority, application France, Oct. 14, 1963, 950,527, Patent 1,388,726 12 Claims. (Cl. 6210) The present invention relates to a process by which a chamber connected to a source of gas is maintained under vacuum by gas entering the chamber being deposited in the solid state on a device for supplying cold by indirect heat exchange with at least one liquefied refrigerating fluid, in which the solid deposits of this gas on the means supplying cold are periodically liquefied, at least in part, by warming up of this latter and are discharged from the chamber.

Processes of this type are more especially employed for ensuring rapid discharges of gas with considerable rates of flow for the purpose of aerodynamic studies. The conduit in which it is desired to ensure the rapid discharge flow is connected at one end to a source of the said gas and at the other end to a chamber under vacuum, in which this gas is deposited in the solid state in pro portion as it reaches the said chamber. This chamber is generally known under the name of cryopump; the vacuum which obtains therein should generally be not more than 0.1 to 0.01 millibar. The gas of which it is desired to ensure the flow is generally deposited on metal plates having good thermal contact with the ducts in which circulates a liquefied refrigerating fluid formed by a gas which is more volatile than the gas which is to be deposited in the solid state. One or more other refrigerating fluids can be used for assuring a preliminary cooling of the gas which enters into the vacuum chamber. For example, if it is desired to assure a flow of nitrogen, this gas can be solidified by heat exchange with liquid hydrogen, after a first cooling by heat exchange with liquid nitrogen. If it is desired to assure a flow of hydrogen, it can be solidified by heat exchange with liquid helium, after a first cooling by heat exchange with liquid hydrogen and optionally liquid nitrogen.

Nevertheless, the heat exchange between the gas to he solidified and the more volatile refrigerating fluid becomes less satisfactory as soon as the solid layer on the heat exchange plates has reached a certain thickness, so that the gas intake capacity of the cryopump decreases. It is then expedient to regenerate the heat exchange arrangement by a warming up which is sufficient to melt the solid deposits on the plates. A relatively hot fluid is then caused to pass through the heat exchange ducts, this ensuring the melting of the solid layer deposited on the heat exchange plates. The liquid formed is then discharged from the chamber, the latter is once again placed under vacuum by means of an auxiliary vacuum pump and then it is put again into operation by re-establishing the circulation of the refrigerating fluids.

If it is desired to ensure continuous operation of the cryopump, it is of course suflicient to provide two Vacuum chambers in parallel, one of which is in operation while the other is undergoing regeneration.

However, it will be understood that the periodic regeneration of the heat exchange plates of the chamber involves a considerable loss of cold and as a consequence an appreciable energy consumption for re-est'ab'lishing the cold state of the chamber after each regeneration, since the chamber must be cooled from a temperature which is higher than the melting point of the gas to be deposited in the solid state down to a temperature such that its 3,362,174 Patented Jan. 9, 1968 vapour pressure by sublimation does not exceed the desired value, i.e., the chamber must be cooled several tens of degrees, at a temperature level (liquefaction point of hydrogen or helium, for example) at which any production of cold requires a high energy consumption.

The present invention has for its object to overcome this disadvantage and to reduce to a large degree the energy consumption which is necessary to ensure the operation of a cryopump. It permits of recovering a considerable fraction of the cold which was hitherto lost because of the evacuation of the liquid formed by the melting of the solid deposits on the heat exchange plates during their regeneration. In addition, it is possible therewith to facilitate the liquefaction of the more volatile refrigerating fluid provided for ensuring the solidification of the gas to be drawn into the cryopump.

The invention is characterised in that the liquid formed during the warming up of the solid deposits, after the said liquid has been withdrawn from the chamber, is vapourised and optionally warmed up so as to recover some of the supply of cold and to utilize the recovered cold to effect the deposition in the solid state of the gas entering the chamber.

The invention moreover preferably comprises the following embodiments, separately or in any combination:

(a) the liquid formed during the heating of the solid deposits is vapourised by heat exchange with the more volatile refrigerating fluid;

(b) the vapourisation according to (a) is effected under vacuum, at a lowest possible temperature level;

(0) the gas formed following the vapouris ation according to (a) and optionally (b) is warmed up in heat exchange with a second refrigerating fluid which is less volatile than the first;

(d) the liquid formed during the warming up of the solid deposits is vapourised in heat exchange with the chamber to be kept under vacuum, as auxiliary refrigerating fluid;

(e) the second refrigerating fluid is the same gas as that to be deposited in the solid state in the chamber, and the liquid formed during the warming up of the solid deposits is combined with this second liquefied refrigerating fluid.

Other features and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawing, relating to a refrigerating installation for a cryopump, designed to permit the deposition by solidification of considerable rates of flow of nitrogen in a chamber maintained at a pressure lower than 0.1 millibar. In this installation, the production of cold is assured by two cycles, the first using nitrogen as refrigerating fluid and the second using hydrogen.

In this installation, the chamber to be kept under vacuum is connected alternately to one or other of the cryopumps 1 and 2, one of these latter 1 being in operation while the other 2 is undergoing regeneration during the period of operation which is illustrated.

Each of these cryopumps, connected to the chamber in which it is desired to assure the flow of nitrogen through a conduit 1A or 2A, is equipped with metal plates formed with ducts in which the refrigerating fluids circulate. A first system of plates shown diagrammatically at 5, 6 is connected to the refrigeration cycle for the production of liquid nitrogen; a second system of plates 3, 4 is connected to the refrigerating cycle for the production of liquid hydrogen.

Each of the cryopumps is provided in its lower part with a receiver 7, 8, in which is to be collected the liquefied nitrogen formed with the defrosting of the plates 3, 4 of the liquid hydrogen cycle, the said tanks being connected by a discharge valve 9, and conduits 17, 18, 19 to the liquid nitrogen storage reservoir 20. A coil 70, 8a disposed in the receiver ensures the melting of the blocks of solid nitrogen which would become detached from the plates before complete melting and would pose the danger of obstructing the valves or discharge conduits. The tanks 7, 8 are in addition connected by valves 11, 12 and conduits 13, 14 to a vacuum pump 15, designed to ensure the preliminary vacuum in the cryopump at the moment of starting up and to eliminate continuously those gases (neon, hydrogen, helium) which cannot be condensed and which are contained in the nitrogen to be pumped. Finally, the heat insulation of the cryopumps is assured by means of double Walls equipped with liquid nitrogen coils 107 and 108.

The nitrogen cycle provided for ensuring the preliminary cooling of the nitrogen to be deposited in the cryopump down to a temperature of about 90 K. is of a known type. The nitrogen recycled through the pipe 74 is brought by the compressor 21 to a pressure of approximately 80 bars absolute. Discharged from the compressor through the pipe 22, it is divided into two parts. The first part is cooled in the exchanger 24 to approximately 93 K. in counter-current with the nitrogen discharged under vacuum (absolute pressure of about 120 millibars) by the pump 102 after vapourisation in heat exchange with the hydrogen cycle in the region of 63 K., which is the temperature of the triple point of nitrogen.

The second part of the nitrogen is cooled in the first place in the exchanger 23 to 196 K. in counter-current with the recycled nitrogen; one fraction is then conducted through the pipe 25 to the expansion machine 26, where it is expanded to approximately 1.3 bars and is cooled to about 80 K., then combined with the gaseous nitrogen originating from the operating cryopump and with the nitrogen vapours originating from the liquid nitrogen reservoir; the combined flow is then recycled through the pipe 72 in counter-current into the exchanger 28 in order to ensure the cooling of the residual part of the nitrogen under pressure to about 155 K.

The two parts of nitrogen under pressure are then combined in the pipe 29, expanded in the valve 30 to approximately 1.3 bars absolute and introduced in the liquid state into the reservoir 20. The nitrogen vapours evolved in this reservoir following the expansion or because of the heat leak are discharged through the pipes 70 and 71 towards the cold end of the exchanger 28.

The hydrogen cycle permitting the final temperature of 33 K. to be reached in the operating cryopump is also of a known type, with production of cold by two expansions with external work at difierent temperature levels.

The hydrogen recycled through the pipe 98 is brought by the compressor 40 to a pressure of about 25 bars absolute. It is introduced by way of the pipe 41 into the exchanger 42, in counter-current with the low-pressure hydrogen recycled from the cryopump undergoing defrosting, and then through the pipe 43 into the exchanger 44, where it is cooled to about 75 in heat exchange with the low-pressure hydrogen recycled from the operating cryopump and the expansion machines.

The hydrogen under pressure then passes by Way of the pipe 45 into the exchanger 46, where it is cooled to approximately 66 K. by vapourisation of liquid nitrogen at 120 millibars absolute. A first fraction thereof is then sent through the pipe 47 to the expansion turbine 48 in which it is expanded to about atmospheric pressure, then combined by means of the pipe 49 with the recycled low-pressure hydrogen and introduced with the latter through the pipe 88 into the exchanger 56.

The remaining hydrogen under pressure is introduced through the pipe 50 into the exchanger 51 and cooled to 51 K. by the recycled low-pressure hydrogen. A fresh fraction thereof is then diverted and sent through the pipe 52 to the expansion turbine 53 in which it is expanded to about atmospheric pressure; cooled to 21 K., at about the dew point of the hydrogen, it is combined by means of the pipe 54 with the hydrogen vapourised in the operating cryopump and returned with said hydrogen to the cold end of the exchanger 58.

The hydrogen under pressure is then sent successively through the pipes 55 and 57 into the exchangers 56 and 58, where it is cooled to about 25 K. by heat exchange with the low-pressure hydrogen originating from the operating cryopump and the expansion engines. It is then returned through the pipe 59 into the operating cryopump.

In the operating cryopump 1, the preliminary cooling to K. of the nitrogen which is drawn in is ensured by the vapourisation under atmospheric pressure in the ducts of the heat exchange plates 5 of liquid nitrogen introduced through the pipe 60, the open valve 61 (the valve 62 connected to the plates 6 of the cryopump 2 undergoing regeneration being closed) and the pipe 63. The vapourised nitrogen is discharged through the pipe 65, the open valve 67 (the corresponding valve 68 connected to the cryopump 2 being closed) and the pipe 69 towards the pipe 71 for the recycling of the cold nitrogen at low pressure.

Moreover, the coils 107 and 108, providing part of the heat insulation of the cryopumps, are fed with liquid nitrogen drawn off through pipe 103 from pipe 60, then sent respectively through pipes 105 and 106 to coils 107 and 108. The vapourised nitrogen at the outlet of coils 107 and 108 is withdrawn through pipe 109 and added to the low pressure nitrogen recycle stream of pipe 73 at the cold end of heat exchanger 23.

The final cooling to 33 K. in the cryopump 1, causing the freezing of the drawn-in nitrogen, is assured by the vapourisation at 20 K. under atmospheric pressure in the ducts of the heat exchange plates 3 of liquid hydrogen introduced through the pipe 59, the open expansion valve 75 (the corresponding valve 76 connected to the plates 4 of the cryopump 2 being closed) and the pipe 77. The vapourised hydrogen is discharged through the pipe 79, the open valve 83 (the corresponding valve 84 being closed) and the pipe 85 towards the cold end of the exchanger 58 of the hydrogen liquefaction cycle.

In the cryopump 2 undergoing regeneration, the melting of the solidified nitrogen deposited on the plates 4 cooled with liquid hydrogen is assured as follows. The low-pressure hydrogen warmed up in the exchanger 44 to approximately K. is sent through the pipe 91 and the open valve 94 (the valve 93 connected to the corresponding cycle of the cryopump 1 being closed) and then through the pipe 96 into the coil 8a in the sump 8 of the cryopump, where it provides for the melting of the blocks of solid nitrogen which could become detached from the plates 4 before complete melting; it then passes into the ducts of the plates 4, thereby ensuring the progressive warming up of the latter to 80 K. It is then discharged through the pipe 80, the open valve 82 (the corresponding valve 81 connected to the hydrogen circuit of the operating cryopump 1 being closed) and the conduit 97 towards the cold end of the exchanger 42, before being heated therein to the region of ambient temperature, and then sent to the intake of the hydrogen compressor.

During the regeneration of the cryopump 2, the major part of the solid nitrogen deposited on the plates 4 is liquefied and flows into the tank 8. It is sent from thence through the open valve 10 and the pipes or conduits 18 and 19 to the liquid nitrogen storage reservoir, with a view to being used for supplying cold, either in the precooling plate 5 or 6 of the cryopumps, or in the hydrogen and nitrogen refrigerating cycles in the exchangers 46 and 24 already referred to. On the other hand, a certain quantity of solid nitrogen is sublimed and produces a raising of the pressure in the cryopump. When the deposits of solid nitrogen are completely eliminated, the residual gaseous nitrogen is removed by the receiver 8,

being brought into communication with the vacuum pump by opening the valve 12.

It will be understood that numerous modifications can be incorporated into the diiferent parts of the foregoing installation without departing from the scope of the invention. In particular, other refrigerating fluids than liquid nitrogen and hydrogen can be used, obviously while taking into account the condition of bringing the heat exchange plates to a temperature which assures the deposition of the nitrogen to be pumped (or optionally of the other gas to be pumped) below the solidification point of the said nitrogen. The refrigerating cycles which are employed can be modified to a certain degree, for example, by only carrying out a single expansion with external work on the hydrogen circuit. Finally, the cold of the liquid nitrogen recovered with the reheating of the cryopump can be partly recovered in a different way, for example, by passage in a coil disposed as a heat shield in a jacket ensuring the heat insulation of the cryopumps.

What we claim is:

1. A process for condensing normally gaseous medium under subatmospheric conditions in alternating chambers, comprising (1) condensing said gaseous medium in one of said alternating chambers by indirect heat exchange with a plurality of refrigerating liquids of distinctly different boiling points in closed separate refrigerating circuits while maintaining said one chamber under subatmospheric conditions, said closed refrigerating circuits being included in each of said alternating chambers, (2) withdrawing thus condensed gas from said other chamber, (3) vaporizing a portion of said withdrawn condensed gas to produce at least a portion of the refrigeration for one of the circuits in one of said chambers, (4) passing another portion of said withdrawn condensed gas in heat exchange with at least one of said refrigerating circuits, and (5) alternating the flow of the gaseous medium so that it is condensed as in step (1) in the other chamber and is withdrawn from the one chamber as in step (2) above.

2. A process as claimed in claim 1, in which the condensed gas outside the chambers is in liquid phase, and said vaporization is conducted at least in part in jackets providing thermal insulation for the chambers.

3. A process as claimed in claim 1, said condensation comprising solidification.

4. A process as claimed in claim 3, and melting the solid in the chambers to form a liquid, and removing the latter liquid from the chambers in liquid phase.

5. A process as claimed in claim 1, in which said vaporization is conducted at least in part by heat exchange with the most volatile said refrigerating fluid.

6. A. process as claimed in claim 5, in which said vaporization is effected in vacuo.

7. A process as claimed in claim 1, and warming the gas resulting from said vaporization to about ambient atmospheric temperature to produce refrigeration, and supplying the refrigeration thus produced to said chambers.

8. A process as claimed in claim 7, in which said warming is conducted at least in part by heat exchange with a refrigerating fluid less volatile than the most volatile refrigerating liquid.

9. A process as claimed in claim 1, in which said withdrawn condensed gas is in admixture with a said refrigerating liquid during said vaporization.

10. A process as claimed in claim 9, in which said withdrawn condensed gas and its admixed said refrigerating liquid are both of substantially the same composition.

11. A process as claimed in claim 1, one of said refrigerating liquids being nitrogen and the other being a liquid boiling lower than nitrogen.

12. A process as claimed in claim 11, said other refrigerating liquid being hydrogen.

References Cited UNITED STATES PATENTS 2,568,223 9/1951 De Baufre 6241 X 2,784,572 3/1957 Wucherer et al. 6241 X 2,822,675 2/1958 Grenier 6241 X 2,897,656 8/1959 Van Der Ster 6240 2,900,798 8/ 1959 Jonkers 6240 X 2,906,101 9/1959 McMahon et a1. 626 2,909,903 10/ 1959 Zimmermann 6240 X 2,919,556 1/ 1960 Mulder 6240 X 2,933,901 4/1960 Davison 6240 X 2,960,834 11/1960 Kirk Patrick 6240 X 3,143,406 8/1964 Becker 6241 X 3,154,394 10/1964 Van Der Ster 6241 X 3,210,952 10/1965 Strom 6240 3,214,924 11/1965 Van Geuns et a1. 62--6 FOREIGN PATENTS 69,438 6/ 1949 Denmark.

NORMAN YUDKOFF, Primary Examiner. V. W. PRETKA, Assistant Examiner. 

1. A PROCESS FOR CONDENSING NORMALLY GASEOUS MEDIUM UNDER SUBATMOSPHERIC CONDITIONS IN ALTERNATING CHAMBERS, COMPRISING (1) CONDENSING SAID GASEOUS MEDIUM IN ONE OF SAID ALTERNATING CHAMBERS BY INDIRECT HEAT EXCHANGE WITH A PLURALITY OF REFRIGERATING LIQUIDS OF DISTINCTLY DIFFERENT BOILING POINT IN CLOSED SEPARATE REFRIGERATING CIRCUITS WHILE MAINTAINING SAID ONE CHAMBER UNDER SUBATMOSPHERIC CONDITIONS, SAID CLOSED REFRIGERATING CIRCUITS BEING INCLUDED IN EACH OF SAID ALTERNATING CHAMBERS, (2) WITHDRAWING THUS CONDENSED GAS FROM SAID OTHER CHAMBER, (3) VAPORIZING A PORTION OF SAID WITHDRAWN CONDENSED GAS TO PRODUCE AT LEAST A PORTION OF THE REFRIGERATION FOR ONE OF THE CIRCUITS IN ONE OF SAID CHAMBERS, (4) PASSING ANOTHER PORTION OF SAID WITHDRAWN CONDENSED GAS IN HEAT EXCHANGE WITH AT LEAST ONE OF SAID REFRIGERATING CIRCUITS, AND (5) ALTERNATING THE FLOW OF THE GASEOUS MEDIUM SO THAT IT IS CONDENSED AS IN STEP (1) IN THE OTHER CHAMBER AND IS WITHDARWN FROM THE ONE CHAMBER AS IN STEP (2) ABOVE. 